(a) Field of the Invention
The present invention relates to a method for preparing cerium carbonate that can improve yield or productivity of cerium carbonate and enables preparation of cerium carbonate having uniform diameter, cerium carbonate, and a method for preparing cerium oxide.
(b) Description of the Related Art
Cerium oxide powder is a high functional ceramic material widely used as a catalyst, a phosphor, cosmetics, an abrasive, etc., and it has been recently spotlighted as an abrasive for a CMP (Chemical Mechanical Polishing) process in the field of semiconductor device.
In general, the cerium oxide powder can be prepared by a liquid-phase method, a gas-phase method or a solid-phase method.
According to the liquid-phase method, a pH control agent such as ammonia is added to starting material, i.e., trivalent or tetravalent cerium salt to directly prepare cerium oxide from cerium salt. Although this method is economical because raw material cost and equipment cost is comparatively low, it is difficult to control particle growth because a reaction between starting materials easily occurs from nucleation stage. And, if fine cerium oxide prepared by the liquid-phase method is used as an abrasive, a polishing rate is low thus unfavorable for a continuous process to decrease productivity.
According to the gas-phase method, a cerium metal salt precursor is vaporized and then bonded with oxygen, etc. to directly prepare cerium oxide. This method includes flame combustion decomposition, gas condensation decomposition, plasma vaporization, laser vaporization, etc. However, this method has difficulty in terms of massification because costs of the cerium metal salt precursor and equipment are high, and the study thereof is still under progress.
Meanwhile, according to the solid-phase method, precursor material is fired at high temperature to prepare cerium oxide. As the precursor, cerium carbonate is widely used, and the physical properties and shape of cerium oxide can be varied depending on the kind and shape of cerium carbonate. Thus, in order to control the physical properties (for example, polishing performance of cerium oxide, etc,) or shape, etc. of cerium oxide, a method for preparing cerium carbonate that can easily control the kind or shape of cerium carbonate is required.
However, a method for preparing cerium carbonate with simply controlling the kind, shape or size has not been sufficiently developed yet, and diameter of cerium carbonate obtained by the existing preparation method has insufficient uniformity of diameter.
Moreover, a method for preparing cerium carbonate known so far has a disadvantage of insufficient yield or productivity, and in case cerium carbonate with a specific shape or crystal structure such as orthorhomabic structure is to be obtained, a high pressure reaction is required, which involves dangerousness.